Rosiglitazone increases fatty acid Δ9-desaturation and decreases elongase activity index in human skeletal muscle in vivo.

The ratio of unsaturated to saturated long-chain fatty acids (LC-FAs) in skeletal muscle has been associated with insulin resistance. Some animal data suggest a modulatory effect of peroxisome proliferator receptor γ (PPARγ) stimulation on stearoyl-CoA desaturase 1 (SCD1) and LC-FA composition in skeletal muscle, but human data are rare. We here investigate whether treatment with a PPARγ agonist affects myocellular SCD1 expression and modulates the intramyocellular fatty acid profile in individuals with impaired glucose tolerance. Muscle biopsies and hyperinsulinemic-euglycemic clamps were performed in 7 men before and after 8 weeks of rosiglitazone treatment. Intramyocellular saturated, monounsaturated, and polyunsaturated intramuscular fatty acid profiles were measured by gas chromatography. Effects on SCD1 messenger RNA expression were analyzed in C2C12 cells and in human biopsies before and after rosiglitazone treatment. As expected, treatment with the PPARγ activator rosiglitazone improved insulin sensitivity in humans. Myocellular SCD1 messenger RNA expression was increased in human biopsies and C2C12 cells. Although the total content of myocellular LC-FA was unchanged, a relative shift from saturated LC-FAs to unsaturated LC-FAs was observed in human biopsies. Particularly, the amount of stearate was reduced, whereas the amounts of palmitoleate as well as oleate and vaccenate were increased, after rosiglitazone therapy. These changes resulted in an increased fatty acid Δ9-desaturation index (16:1/16:0 and 18:1/18:0) in skeletal muscle and a decreased elongase activity index (18:0/16:0). The PPARγ associated phenotypes may be partially explained by an increased Δ9-desaturation and a decreased elongase activity of skeletal muscle.